Multi-carrier transmission device

ABSTRACT

A multi-carrier transmission device improves peak suppression efficiency in a multi-carrier signal. The multi-carrier transmission device ( 100 ) has a peak suppression unit ( 140 ) for dividing a multi-carrier signal into two parts: a first multi-carrier signal and a second multi-carrier signal. A peak signal detection unit ( 142 ) detects a power value at a predetermined interval concerning the first multi-carrier signal. When the detected power value is equal to or above a predetermined level, a peak extraction unit ( 144 ) extracts a signal component equal to or above the predetermined level from the first multi-carrier signal. A band limit filter unit ( 146 ) passes only a predetermined band from the extracted signal component. An adder ( 154 ) subtracts the signal component after the band limit from the second multi-carrier signal. A multiplier ( 150 ) is arranged at a latter stage of the band limit filter unit ( 146 ) and multiplies a weight for compensating the power loss in the band limit filter unit ( 146 ) and the first multi-carrier signal.

TECHNICAL FIELD

The present invention relates to a multicarrier transmitting apparatus.More particularly, the present invention relates to a multicarriertransmitting apparatus that reduces peaks appearing in multicarriersignals.

BACKGROUND ART

Multicarrier transmission is becoming a focus of attention as ahigh-speed transmission technique that reduces the influence offrequency selective fading caused by multipath channels. In thismulticarrier transmission, sharp power peaks are produced in a generatedmulticarrier signal. When these signals having great peaks are inputtedto a nonlinear amplifier, these signals are amplified in a nonlinearamplifier with nonlinear distortion, and so, these are causes ofdeterioration of transmission characteristics and out-of-band radiationin multicarrier transmission. To prevent this, it is conceivable thatback-off may be provided with a nonlinear amplifier, but, efficiency ofan amplifier deteriorates.

Then, various techniques (e.g. Patent documents 1 and 2) to reduce peaksin multicarrier signals, are proposed.

For example, in Patent Document 2, peak reduction is attempted as thefollowing steps. That is, first, peaks for transmission data aredetected using a threshold, and differential data between the peaks andthe threshold, that is, peak components that are beyond a threshold in asignal, are generated. Second, the generated peak components areband-limited by filter processing. Third, peak components afterband-limiting are subtracted from the original transmission data. Assuch, transmission data where peaks are decreased is formed.

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-185432Patent Document 2: Japanese Patent Application Laid-Open No. 2004-104162DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, with conventional multicarrier transmitting apparatuses, noconsideration is given to power loss in band-limiting in the second stepabove. That is, the peak components generated in the first step have awide bandwidth, and so power loss occurs when band-limiting is carriedout in the second step, and consequently, peak components still remaineven when the peak components after band-limiting are subtracted fromthe original transmission data. Although by repeating this processing,removing peak components is possible, is involved a problem that thenumber of times processing is repeated is many, that is, peak reductionefficiency is bad. Increasing the number of times processing is repeatedleads to circuit scale increase, so that, there is a problem that amulticarrier transmitting apparatus itself becomes larger.

The present invention is made in view of the above-described problems,and it is therefore an object of the present invention to provide amulticarrier transmitting apparatus that makes it possible to improvepeak reduction efficiency in multicarrier signals.

Means for Solving the Problem

The multicarrier transmitting apparatus of the present inventionprovides a peak reduction section that reduces peak power appearing in amulticarrier signal and the peak reduction section adopts aconfiguration including: a power detection section that divides themulticarrier signal into two multicarrier signals and detects powervalues at regular intervals with respect to one multicarrier signal; asignal component extraction section that, when a detected power value isequal to or greater than a predetermined level, extracts a signalcomponent equal to or greater than the predetermined level from the onemulticarrier signal; a band-limiting filter that only allows to pass apredetermined band in the extracted signal component; an adder thatsubtracts the signal component after the band-limiting from the othermulticarrier signal; and a multiplier that is arranged subsequent to theband-limiting filter and that multiplies the other multicarrier signaland a weight for compensation for power loss in the band-limitingfilter.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the present invention, it is possible to provide amulticarrier transmitting apparatus that improves peak reductionefficiency in multicarrier signals.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of the multicarriertransmitting apparatus according to Embodiment 1 of the presentinvention;

FIG. 2 is a block diagram showing a configuration of the peak reductionsection of the multicarrier transmitting apparatus according toEmbodiment 2 of the present invention;

FIG. 3 is a block diagram showing a configuration of the peak reductionsection of the multicarrier transmitting apparatus according toEmbodiment 3 of the present invention;

FIG. 4 is a block diagram showing a configuration of the peak reductionsection of the multicarrier transmitting apparatus according toEmbodiment 4 of the present invention;

FIG. 5 is a block diagram showing a configuration of the peak reductionsection of the multicarrier transmitting apparatus according to otherembodiment of the present invention;

FIG. 6 is a block diagram showing a configuration of the peak reductionsection of the multicarrier transmitting apparatus according to otherembodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below in detailwith reference to the accompanying drawings. Further, in embodiments,the same components are assigned the same reference numerals andoverlapping descriptions are omitted.

Embodiment 1

As shown in FIG. 1, multicarrier transmitting apparatus 100 inEmbodiment 1 has S/P conversion section 110, IFFT section 120, P/Sconversion section 130, peak reduction section 140 and transmissionsection 160. Then, peak reduction section 140 has peak signal detectionsection 142, peak extraction section 144, band limiting filter section146, weight generation section 148, multiplier 150, delay section 152and adder 154.

S/P conversion section 110 receives modulated and encoded transmissiondata as input. This S/P conversion section 110serial-to-parallel-converts the inputted signal, and outputs the signalto IFFT section 120.

IFFT section 120 performs an inverse fast Fourier transform on theinputted signal after serial-to-parallel conversion and outputs theinputted signal after inverse fast Fourier transform to P/S conversionsection 130.

P/S conversion section 130 parallel-to-serial-converts the inputtedsignal after the inverse fast Fourier transform and acquires amulticarrier signal. This multicarrier signal is outputted to delaysection 152 and peak signal detection section 142.

Peak signal detection section 142 detects the instantaneous power of theinputted signal at predetermined timing intervals (i.e. sample timings)and outputs the detected power value at each timing and the multicarriersignal at each timing to peak extraction section 144.

Peak extraction section 144 compares the inputted detected power valueswith the preset threshold value, and, when a detected power value aresmaller than the threshold value, peak extraction section 144 outputs azero to band limiting filter section 146. Moreover, when a detectedpower value is equal to or greater than the threshold value, peakextraction section 144 outputs the signal as the peak signal componentwhere the power related to the threshold is subtracted from the timingof the multicarrier signal to band limiting filter section 146.

Band limiting filter section 146 limits the band of the inputted signaland outputs the peak signal component subjected to band-limiting tomultiplier 150.

Weight generation section 148 outputs the weight for compensation forpower loss of the peak signal component resulting from band-limiting inband limiting filter section 146, to multiplier 150. Here, the presentembodiment uses the weight with a fixed value set in advance.

Multiplier 150 multiplies the peak signal component subjected toband-limiting from band limiting filter section 146 and the weight fromweight generation section 148 and outputs the operation result to adder154.

The output signal outputted from P/S conversion section 130 is dividedinto two routes and delay section 152 gives the multicarrier signal adelay so as to synchronize the time when one multicarrier signal isinputted to adder 154 through peak signal detection section 142, peakextraction section 144, band limiting filter section 146 and multiplier150, and the time when the other multicarrier signal is inputted toadder 154 through delay section 152. That is, the multicarrier signaland the peak signal component are synchronized. Then, the delayedmulticarrier signal is inputted to adder 154.

By subtracting the peak signal components weighted processing from themulticarrier signal inputted through delay section 152, adder 154reduces peaks of the multicarrier signal. The multicarrier signal afterthis peak reduction is applied predetermined processing such as D/Aconversion, frequency conversion and power control and transmitted viaan antenna.

In this way, according to Embodiment 1, multicarrier transmittingapparatus 100 provides peak reduction section 140, and this peakreduction section 140 has: peak signal detection section 142 thatdivides a multicarrier signal into two and detects power values atregular intervals in one multicarrier signal; peak extraction section144 that, when a detected power value is equal to or greater than apredetermined level, extracts signal component which is equal to orgreater than the predetermined level, from one multicarrier signal; bandlimiting filter section 146 that allows to pass only predetermined bandin the extracted signal component; adder 154 that subtracts the signalcomponent after band-limiting from the other multicarrier signal; andmultiplier 150, which is arranged subsequent to band limiting filtersection 146, that multiplies the other multicarrier signal and theweight for compensation for power loss in band limiting filter section146.

By this means, it is possible to subtract (peak) signal components wherepower loss resulting from band-limiting is compensated for, from theoriginal multicarrier signal, so that, speed for removing (peak) signalcomponents becomes faster than in conventional cases. As a result, thenumber of times subtraction of (peak) signal component is repeateddecreases, thereby improving peak reduction efficiency. Furthermore, thenumber of times subtraction of (peak) signal component is repeateddecreases, thereby minimizing the circuit scale and realizingminiaturization and weight reduction of the multicarrier transmittingapparatus.

Embodiment 2

As shown in FIG. 2, the multicarrier transmitting apparatus ofEmbodiment 2 has peak reduction section 210, and peak reduction section210 has peak extraction section 212, power detection section 214, powerloss calculation section 216 and weight generation section 218.

Peak extraction section 212 compares inputted detected power values withthe preset threshold value, and, when a detected power value is smallerthan the threshold value, peak extraction section 212 outputs a zero toband limiting filter section 146 and the detected power value to powerloss calculation section 216. Moreover, when the detected power value isequal to or greater than a threshold value, peak extraction section 212outputs the detected power value to power loss calculation section 216and outputs the signal as the peak signal component where the powerrelated to the threshold is subtracted from the timing of themulticarrier signal, to band limiting filter section 146.

Power detection section 214 detects the power value of the peak signalcomponent after band-limiting, which is the output from band limitingfilter section 146, and outputs the detected power value to power losscalculation section 216.

Power loss calculation section 216 receives the power value from peakextraction section 212, that is, the power value which is detected atpredetermined timing (i.e. sample timing) in peak signal detectionsection 142 and which is equal to or greater than the preset threshold,and receives a power value with the same timing from power detectionsection 214. Then, using the inputted detected power values, power losscalculation section 216 calculates the integral of the differencebetween the detected power value of the peak signal component to beinputted to the band-limiting filter and the detected power value of thepeak signal component over a predetermined period (e.g. 1 OFDM symbol),that is, calculates the power loss over the predetermined period in bandlimiting filter section 146. This value of power loss (power loss value)is outputted to weight generation section 218.

Based on the inputted power loss value, weight generation section 218calculates a weight for compensation for power loss of the peak signalcomponent resulting from band-limiting in band limiting filter section146 and outputs the calculated weight to multiplier 150. That is, theweight calculated in weight generation section 218 is updated on a perabove predetermined period basis (i.e. 1 OFDM symbol).

In this way, according to Embodiment 2, multicarrier transmittingapparatus provides peak reduction section 210, and this peak reductionsection 210 has: peak signal detection section 142 that divides amulticarrier signal into two and detects power values at regularintervals in one multicarrier signal; peak extraction section 212 that,when a detected power value is equal to or greater than a predeterminedlevel, extracts signal component which is equal to or greater than thepredetermined level, from one multicarrier signal; band limiting filtersection 146 that allows to pass only predetermined band in the extractedsignal component; adder 154 that subtracts the signal component afterband-limiting from the other multicarrier signal; and multiplier 150,which is arranged subsequent to band limiting filter section 146, thatmultiplies the other multicarrier signal and the weight for compensationfor power loss in band limiting filter section 146. Additionally, themulticarrier transmitting apparatus provides weight generation section218 that forms a weight in accordance with the difference between thepower value of the signal component before band-limiting and the powervalue of the signal component after band-limiting in band limitingfilter section 146.

By this means, it is possible to subtract (peak) signal componentscompensated for by weights formed based on power loss derived from powervalues before and after band-limiting, from the original multicarriersignal, so that, speed of removing (peak) signal components becomesstill faster than in Embodiment 1. As a result, the number of timessubtraction of (peak) signal component is repeated decreases, therebyimproving peak reduction efficiency. Furthermore, the number of timessubtraction of (peak) signal component is repeated decreases, therebyminimizing the circuit scale and realizing miniaturization and weightreduction of the multicarrier transmitting apparatus.

Embodiment 3

As shown in FIG. 3, the multicarrier transmitting apparatus ofEmbodiment 3 has peak reduction section 310, and peak reduction section310 has peak signal component fitting section 312 and weight generationsection 314.

Peak signal component fitting section 312 changes a weight candidatesequentially and determines the weight candidate so as to minimize adifference between a peak signal component from peak extraction section212 and result of multiplying the weight candidate and a peak signalcomponent after band-limiting. That is, peak signal component fittingsection 312 changes the weight candidate sequentially, fits the resultof multiplying the weight candidate and the peak signal component afterband-limiting, with the peak signal component from peak extractionsection 212 and determines the optimal weight. To be more specific, peaksignal fitting component section 312 determines the weight such that,the difference between the waveform of the peak signal component frompeak extraction section 212 (i.e. waveform of amplitude value in thetime domain) and the waveform of the result of multiplying the weightcandidate and the peak signal component after band-limiting is minimumover a predetermined period (e.g. 1 OFDM symbol). Incidentally, here,the weight candidate which the difference is minimum using the leastsquare method is determined as optimal weight.

Weight generation section 314 forms the weight in accordance with theweight determined in peak signal component fitting section 312 andoutputs the formed weight to multiplier 150.

Incidentally, although a case has been explained with the aboveexplanation where peak signal component fitting section 312 fits allsample points in peak signal components, that is, all sampling timingsover a predetermined period (e.g. 1 OFDM symbol), the present embodimentis not limited to this, and an optimal weight may be determined so as tomatch a peak signal component before band-limiting and a peak signalcomponent after band-limiting in a sample point, for example, the samplepoint where the detected power value in the peak signal component beforeband-limiting is maximum.

In this way, according to Embodiment 3, multicarrier transmittingapparatus provides peak reduction section 310, and this peak reductionsection 310 has: peak signal detection section 142 that divides amulticarrier signal into two and detects power values at regularintervals in one multicarrier signal; peak extraction section 212 that,when a detected power value is equal to or greater than a predeterminedlevel, extracts signal component which is equal to or greater than thepredetermined level, from one multicarrier signal; band limiting filtersection 146 that allows to pass only predetermined band in the extractedsignal component; adder 154 that subtracts the signal component afterband-limiting from the other multicarrier signal; and multiplier 150,which is arranged subsequent to band limiting filter section 146, thatmultiplies the other multicarrier signal and the weight for compensationfor power loss in band limiting filter section 146.

Additionally, the multicarrier transmitting apparatus provides: peaksignal component fitting section 312 that changes a weight candidatesequentially and fits the waveform of the signal of multiplying eachweight candidate and the peak signal component after band-limiting, withthe waveform of peak signal components before band-limiting, andspecifies the weight candidate which minimizes the difference of theboth waveforms; and weight generation section 314 that forms a weightrelated to the specified weight candidate.

By this means, it is possible to subtract (peak) signal componentscompensated for by the optimal weight such that the difference of thewaveform before and after band-limiting is minimum, from the originalmulticarrier signal, so that, speed of removing (peak) signal componentsbecomes still faster than in Embodiment 1. As a result, the number oftimes subtraction of (peak) signal component is repeated decreases,thereby improving peak reduction efficiency. Furthermore, the number oftimes subtraction of (peak) signal component is repeated decreases,thereby minimizing the circuit scale and realizing miniaturization andweight reduction of the multicarrier transmitting apparatus.

Moreover, the above multicarrier transmitting apparatus may alsoprovide: peak signal component fitting section 312 as a weightcalculation section, that calculates the weight which matches the powervalue of the signal component before band-limiting, and the value ofmultiplying power value of the signal component after band-limiting andthe weight related to the signal component after band-limiting; andweight generation section 314 that forms a calculated weight.

By this means, the sample point at a predetermined timing is only to befitted, thereby reducing an amount of calculation processing.

Embodiment 4

As shown in FIG. 4, the multicarrier transmitting apparatus ofEmbodiment 4 has peak reduction section 410, and this peak reductionsection 410 has weight generation section 412.

When a detected power value in each sample point is equal to or greaterthan a threshold value, weight generation section 412 inputs thedetected power value outputted from peak extraction section 212, andforms a weight in accordance with this detected power values. To be morespecific, weight generation section 412 forms a weight in proportion toan inputted detected power value. By this means, in the timings ofoccurrence of peaks, the weights are updated on a per sample timingbasis (i.e. the timing shorter than 1 OFDM symbol).

Incidentally, although a case has been described here where a weight isformed in accordance with a detected power value, if, instead of power,amplitude is detected in peak signal component detection section 142,weight generation section 412 inputs a detected amplitude valueoutputted from peak extraction section 212 when the detected amplitudevalue in each sample point is equal to or greater than a thresholdvalue, and may also form a weight in accordance with this detectedamplitude value.

Moreover, incidentally, weight generation section 412 may also form aweight in accordance with a detected power value detected in powerdetection section 214, instead of the output from peak extractionsection 212. Moreover, as well as this case, if, instead of power,amplitude is detected in power detection section 214, weight generationsection 412 may also form a weight in accordance with this detectedamplitude value.

In this way, according to Embodiment 3, multicarrier transmittingapparatus provides peak reduction section 410, and this peak reductionsection 410 has: peak signal detection section 142 that divides amulticarrier signal into two and detects power values at regularintervals in one multicarrier signal; peak extraction section 144 that,when a detected power value is equal to or greater than a predeterminedlevel, extracts signal component which is equal to or greater than thepredetermined level, from one multicarrier signal; band limiting filtersection 146 that allows to pass only predetermined band in the extractedsignal component; adder 154 that subtracts the signal component afterband-limiting from the other multicarrier signal; and multiplier 150,which is arranged subsequent to band limiting filter section 146, thatmultiplies the other multicarrier signal and the weight for compensationfor power loss in band limiting filter section 146.

Then, this multicarrier transmitting apparatus further provides weightgeneration section that forms weights in accordance with power values ofsignal components before band-limiting or after band-limiting in bandlimiting filter section 146.

By this means, weights are formed in accordance with power valuesthemselves detected before or after band-limiting, so that weights canbe changed more adaptively (i.e. changing weights on a per sample pointbasis in the above explanation). Signal components (peak signalcomponents) compensated for by these weights can be subtracted from theoriginal multicarrier signal, so that speed of removing (peak) signalcomponents becomes still faster. As a result, peak reduction efficiencyis improved, thereby decreasing the number of times subtraction of(peak) signal component is repeated.

Other Embodiment

Although cases have been explained with Embodiments 1 and 4 where weightmultiplying processing is performed after band-limiting, weightmultiplying processing may also be performed before band-limiting.

(1) When a case is applied to Embodiment 1, this multicarriertransmitting apparatus has peak reduction section 510 as shown in FIG.5, and this peak reduction section 510 has multiplier 512 and bandlimiting filter section 514.

Multiplier 512 is arranged prior to band limiting filter section 514,multiplies an output signal from peak extraction section 144 and aweight formed in weight generation section 148 and outputs the result toband limiting filter section 514. Similar to Embodiment 1, this weightis for compensation for power loss resulting from band-limiting of peaksignal components in band limiting section 514.

In this way, according to the present embodiment, multicarriertransmitting apparatus provides peak reduction section 510, and thispeak reduction section 510 has: peak signal detection section 142 thatdivides a multicarrier signal into two and detects power values atregular intervals in one multicarrier signal; peak extraction section144 that, when a detected power value is equal to or greater than apredetermined level, extracts signal component which is equal to orgreater than the predetermined level, from one multicarrier signal; bandlimiting filter section 514 that allows to pass only predetermined bandin the extracted signal component; adder 154 that subtracts the signalcomponent after band-limiting from the other multicarrier signal; andmultiplier 512, which is arranged prior to band limiting filter section514, that multiplies the other multicarrier signal and the weight forcompensation for power loss in band limiting filter section 514.

(2) Moreover, when a case is applied to Embodiment 4, this multicarriertransmitting apparatus has peak reduction section 610 as shown in FIG.6, and this peak reduction section 610 has weight generation section612, multiplier 614 and band limiting filter section 616.

Weight generation section 612 inputs a detected power value outputtedfrom peak extraction section 212 when the detected power value in eachsample point is equal to or more than a threshold value and forms aweight in accordance with this detected value. To be more specific,weight generation section 612 forms a weight in proportion to theinputted detected power value, for example.

Multiplier 614 is arranged prior to band limiting filter section 616,multiplies an output signal from peak extraction section 212 and aweight formed in weight generation section 612 and outputs the result toband limiting filter section 616. Similar to Embodiment 4, these weightsare for compensation for power loss resulting from band-limiting of peaksignal components in band limiting section 616.

In this way, according to the present embodiment, multicarriertransmitting apparatus provides peak reduction section 610, and thispeak reduction section 610 has: peak signal detection section 142 thatdivides a multicarrier signal into two and detects power values atregular intervals in one multicarrier signal; peak extraction section212 that, when a detected power value is equal to or greater than apredetermined level, extracts signal component which is equal to orgreater than the predetermined level, from one multicarrier signal; bandlimiting filter section 616 that allows to pass only predetermined bandin the extracted signal component; adder 154 that subtracts the signalcomponent after band-limiting from the other multicarrier signal; andmultiplier 614, which is arranged prior to band limiting filter section616, that multiplies the other multicarrier signal and the weight forcompensation for power loss in band limiting filter section 616.

Moreover, the multicarrier transmitting apparatus above provides weightgeneration section 612 that forms a weight in accordance with a powervalue of signal component before band-limiting in band limiting filtersection 616.

INDUSTRIAL APPLICABILITY

The multicarrier transmitting apparatus of present invention is suitablefor use in improving peak reduction efficiency in multicarrier signals.

1. A multicarrier transmitting apparatus comprising a peak reductionsection that reduces peak power appearing in a multicarrier signal, thepeak reduction section comprising: a power detection section thatdivides the multicarrier signal into two multicarrier signals anddetects power values at regular intervals with respect to onemulticarrier signal; a signal component extraction section that, when adetected power value is equal to or greater than a predetermined level,extracts a signal component equal to or greater than the predeterminedlevel from the one multicarrier signal; a band-limiting filter that onlyallows to pass a predetermined band in the extracted signal component;an adder that subtracts the signal component after the band-limitingfrom the other multicarrier signal; and a multiplier that is arrangedsubsequent to the band-limiting filter and that multiplies the othermulticarrier signal and a weight for compensation for power loss in theband-limiting filter.
 2. The multicarrier transmitting apparatusaccording to claim 1, comprising a weight formation section that formsthe weight in accordance with a difference between the power value ofthe signal component before the band-limiting and the power value of thesignal component after the band-limiting in the band-limiting filter. 3.The multicarrier transmitting apparatus according to claim 1, furthercomprising: a fitting section that changes weight candidatessequentially, fits a waveform of signals derived by multiplying thesignal component after the band-limiting by the weight candidates, witha waveform of the signal component before the band-limiting, andspecifies the weight candidate that minimizes a difference of thewaveforms; and a weight formation section that forms the weight relatedto the specified weight candidate.
 4. The multicarrier transmittingapparatus according to claim 1, further comprising: a weight calculationsection that calculates the weight that matches the power value of thesignal component before band-limiting, and the value of multiplying theweight and the power value of the signal components after band-limiting;a weight formation section that forms the calculated weight.
 5. Themulticarrier transmitting apparatus according to claim 1, furthercomprising a weight formation section that forms the weight inaccordance with the power value of the signal component beforeband-limiting or the power value of the signal component afterband-limiting in the band limiting filter.